Parabolic dish antenna with aperture blocking correction



G. WILKES Jan. l, 1963 PARABoLIc DISH ANTENNA WITH APERTURE BLocKING CORRECTION File@ July 20, 1955 GILBERT w/L K55y l INVENTOR.

Q, Arron/grs UnitedStates Patent Office 3 071 770 PARABOLIC DISH ATENNA WITH APERTURE BLOCKING CORRECTION Gilbert Wilkes, Detroit, Mich., assigner to the United States of America as represented by the Secretary of the Navy Filed July 20, 1953, ser. No. 369,071 3 Claims. (ci. 343-781) This invention relates generally to parabolic dish antennas, and more particularly to an improved feed means for supplying energy to the antenna.

The principle of the invention resides in bringing a small controllable amount of radiation through an antenna feed reflector plate to perform a useful purpose, such as filling in the shadow caused by the feed of center fed reflectors. The shadow or hole in the wave front leaving the reflector is objectionable because of its effect on the beam width and lobe level of the distant field pattern. A certain portion of the source radiation is brought directly from the feed in a forward direction to fill the shadow in the distant field.

It is an object of this invention to provide an arrangement whereby a small controllable amount `of radiation can be brought through a radar feed reflector plate to fill in the shadow caused by the feed of center fed parabolic dish antennas.

Another object of the invention is to provide an arrangement for securing perfect filling of the shadow or hole caused by the feed of center fed parabolic dish antennas which is controllable both as to amount and phase to secure perfect filling of the shadow or hole.

These and other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 shows a waveguide and a parabolic dish or reflector, certain parts being shown in axial section, and embodying the features of the invention;

FIG. 2 shows an enlargement of a portion of the dielectric convex lens of FIG. l; and

FIG. 3 is a cross section taken along the line 3-3 of FIG. 2.

According to the invention, there is provided in a conventional radar having a parabolic dish antenna, an antenna feed comprising a cylindrical waveguide, a dielectric lens of cylindrical shape including a conical impedance matching portion inserted in the waveguide.

4There is also provided a convex dielectric lens mounted at the outer end of the cylindrical lens. A reflecting means having an orifice therein is mounted in the face of the convex lens opposite the dish. The reflecting means is arranged to reflect a major portion of the electromagnetic energy back through the convex lens to the radar dish. An additional means is mounted adjacent to the reflecting means for determining the phase of the portion of electromagnetic energy that passes through the orifice. Thus, the electromagnetic energy passing through the orifice can be controlled both in phase and amount to reduce the shadow caused by the radar feed of a center fed reflector.

Referring now to the figures of the drawings, particularly to FIG. l, there is shcwn a radar feed consisting of a dielectric lens of cylindrical shape, having a conical impedance matching portion 12 at its inner end and carrying a plane reflector 14 and a convex lens 16 at its outer end. The reflector may comprise a metal plate or may suitably be formed of a fllm of conductive paint such as silver. Beyond the reflector 14 there is mounted a dielectric face plate 18 which is utilized to control the phase of the radiation passing through an orifice 20,

shown in FIGS. 2 and 3, in reflector 14. The amount of radiation passing from the radar feed 10 to dielectric face plate 18 is determined by the size of the orifice 20 in reflector 14.

The radar feed 10 is associated with a section of cylindrical waveguide 22 which passes through the center opening 24 of a suitable radar dish antenna 26. A choke 28 may be provided around opening 24, if it is so desired. The waveguide section 22 is mounted for rotation, and it carries the lens 10 and the assemblies affixed thereto along in such rotation. A motor 30 carrying a drive gear 32 on its shaft serves to rotate waveguide section 22 by means of a driven gear 34 which is secured to the waveguide section 22. These elements are conventional, and consequently do not form any novel parts of the present invention. The novelty in the present invention resides in providing the orifice 20 in the plane reflector 14 and in mounting the dielectric face plate adjacent to reflector 14 as pointed out above.

In operation, during transmission, the electromagnetic energy is conducted through the rotating waveguide 22 towards the reflector 14. When the radar feed element 10 is encountered, the electromagnetic energy enters the dielectric through the conical impedance matching portion 12, passes through the cylindrical stem 10 to the reflector 14, where it is then returned through the dielectric lens 16 to the front surface of the radar dish 26. If the rotating waveguide 22 is arranged to form a small angle with its axis of rotation, a useful conical scan is obtained upon rotation of the feed element.

A small portion of the electromagnetic energy passes through the orifice 20 of reflector 14 to the dielectric face plate 18, which is used to control the phase of the radiation. Since both the phase and the amount of radiation can be controlled by controlling the size of the orifice 20 and by placing the dielectric face plate adjacent to the reflector 14, it is possible to perfectly fill in the shadow or hole in the wave front leaving the dish 26.

Another useful result can be obtained from this invention by piping the electromagnetic energy secured from this orifice to a suitable point to secure an auxiliary beam. Thus in some capture problems relating to aerial missiles, it is desirable to have a low level broad beam displaced to one side of the main beam and rotating around the main beam, to obtain a broad spatial coverage. This does not detract from the power and gain of the main beam nearly as much as if the main beam were broadened to secure the same coverage.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An antenna feed for a parabolic dish antenna comprising a cylindrical waveguide extending through the center of the dish antenna, a dielectric lens of cylindrical shape including a conical impedance matching portion aflixed coaxially to said cylindrical lens for receiving electromagnetic energy from said waveguide, said cylindrical lens being mounted within said waveguide with said conical portion extending toward said dish, a convex dielectric lens mounted at the end of said cylindrical lens opposite said conical portion, reflecting means including a thin disk of metal having an orifice therein and mounted substantially adjacent to the face of said convex lens opposite said dish and being of the same diameter as that of said convex lens, said reflecting means being arranged to reflect the major portion of said electromagnetic energy back through said convex lens to said radar dish, and an additional means mounted adjacent Patented Jan. l, 1963 to said reflecting means for determining the phase of the portion of electromagnetic energy that passes through said orice, whereby said radiation passing through said orifice can be controlled both in phase and amount to' reduce to a minimum the shadow in the distant eld caused by the feed. d

2. An arrangement as set forth in claim 1, wherein said reecting means comprises a coatof metallic conducting paint such as silver- VV 3. An arrangement as set forth in claim 1, wherein said additional means for changing the phase of the radiation passing through said orice comprises a dielectric face plate of the same diameter as the diameter of said convex lens.

References Cited in the le of this patent UNITED STATES PATENTS 2,407,690 Southworth Sept. 17, 1946 2,427,098 Keizer Sept. 9, 1947 2,556,087 Iams June 5, 1951 2,617,029 Plummer et al. Nov. 4, 1952 2,736,894 Koch Feb. 28, 1956 

1. AN ANTENNA FEED FOR A PARABOLIC DISH ANTENNA COMPRISING A CYLINDRICAL WAVEGUIDE EXTENDING THROUGH THE CENTER OF THE DISH ANTENNA, A DIELECTRIC LENS OF CYLINDRICAL SHAPE INCLUDING A CONICAL IMPEDANCE MATCHING PORTION AFFIXED COAXIALLY TO SAID CYLINDRICAL LENS FOR RECEIVING ELECTROMAGNETIC ENERGY FROM SAID WAVEGUIDE, SAID CYLINDRICAL LENS BEING MOUNTED WITHIN SAID WAVEGUIDE WITH SAID CONICAL PORTION EXTENDING TOWARD SAID DISH, A CONVEX DIELECTRIC LENS MOUNTED AT THE END OF SAID CYLINDRICAL LENS OPPOSITE SAID CONICAL PORTION, REFLECTING MEANS INCLUDING A THIN DISK OF METAL HAVING AN ORIFICE THEREIN AND MOUNTED SUBSTANTIALLY ADJACENT TO THE FACE OF SAID CONVEX LENS OPPOSITE SAID DISH AND BEING OF THE SAME DIAMETER AS THAT OF SAID CONVEX LENS, SAID REFLECTING MEANS BEING ARRANGED TO REFLECT THE MAJOR PORTION OF SAID ELECTROMAGNETIC ENERGY BACK THROUGH SAID CONVEX LENS TO SAID RADAR DISH, AND AN ADDITIONAL MEANS MOUNTED ADJACENT TO SAID REFLECTING MEANS FOR DETERMINING THE PHASE OF THE PORTION OF ELECTROMAGNETIC ENERGY THAT PASSES THROUGH SAID ORIFICE, WHEREBY SAID RADIATION PASSING THROUGH SAID ORIFICE CAN BE CONTROLLED BOTH IN PHASE AND AMOUNT TO REDUCE TO A MINIMUM THE SHADOW IN THE DISTANT FIELD CAUSED BY THE FEED. 